ADHESIVES
1.
Test First - Unless you have used the adhesive on the same surface before, you can always use this simple test to determine if you are using the right one.
Glue your tesserae on and wait 24 - 48 hrs.
Then try to pry it off.
If it is for a wet application such as outside or in a shower, soak in water overnight , then try to pry off again. If the tesserae does not come off , the adhesive you chose is a winner!
Always read the label first. Not only does it usually contain some very helpful information, it usually provides a toll-free number should you have any questions about its use or safety. Always check the chemicals you are working with, especially if you are pregnant or have any respiratory ailment. In those cases, a special mask may be called for. Talk to your doctor.
Tile Mastic
Use over wood, tile (yes, you can tile over tile), Formica, ceramic.
Will not stick to metal or concrete.
Not waterproof.
Mortar based Thin-set - Thin-set is a mortar based adhesive you can mix with water OR an acrylic additive.
Best choice for concrete (stepping stones, birdbaths), terra cotta, and backer boards.
Will not stick to metal or other non-porous surfaces without special preparation.
It is the only adhesive you can use to really 'float' tiles. This means you can build up the adhesive under a thinner piece of tile so that it is flush with the tile next to it.
Totally waterproof.
Dries white or gray (know which color you are buying before purchase).
Do not empty into sink or drain. Seriously! You will regret it when you have to replace your pipes.
Read the bag! Everything I know about thin-set came from the back of the bag.
Mix with an acrylic additive instead of water to increase its strength and flexibility, and speed drying time. I prefer using the additive.
WeldBond
Similar to PVA glues (below) only stronger.
Waterproof per the manufacturer's literature.
Dries clear.
Sticks to anything (score smooth surfaces).
WeldBond can be purchased on this site on our Tools page.
For more info about WeldBond, visit the manufacturer's website at Frank T. Ross & Sons and click on the WeldBond button at the top left of the screen.
Cleans up with water when still white.

"Weldbond will work vertically if you do a little trick I found. I know you have that lovely blue painter's tape. Put it over the tesserae you want to glue to something vertical and it will hold them in place until the Weldbond sets up. Then just rip it off.
It works really well on bowling balls and vertical surfaces that can't be made horizontal. Plus, I've found that if the tesserae comes off with the tape, it means it would have come off during grouting - so I know where to add that little bit of extra glue!" From techsupport!

PVA Glues (white glue like Elmer's and other craft glues)
Sticks very well to wood that is unfinished
Must prep painted or stained surfaces (see Surfaces).
Can be used with ceramic, porcelain and glass tiles. At least one surface needs to be porous.
Dries clear
Not waterproof.
Safe for children to use.
Easy clean up with water.
Liquid Nails for Small Projects
My favorite for outdoors when I do not want to mix thin-set.
Stick to almost anything, including metal, terra cotta pots, concrete, etc.
Very short "bowl time" (elapsed time before product sets up and can no longer be used)
Always use gloves - serious chemicals.
Cleans up with solvent.
Clear Liquid Nails or Clear Silicone
My choice for 'see-thru' projects such as candle votives and hurricane lanterns.
Most are waterproof. Read the label or call the manufacturer.
Epoxy Glue
I reserve Epoxy for very unique applications which include: gluing cup handles or other vulnerable elements, heavy pieces that just slide off with other glues (may also need to be held or taped in place until glue sets), or it will be exposed to a lot of water.
Completely waterproof.
Epoxy is a two-part glue that has to be mixed (resin + hardener). My favorite is 'Power Poxy' from Home Depot as it is very thick.
Epoxy has a short 'bowl time'. Mix only enough to use in 7 - 10 minutes.
It is almost impossible to clean off once it has dried. It will last forever.
Not recommended for everyday use.
Adhesive Tips
Have you ever opened a tube of glue only to find it has dried up and even poking a nail or paperclip didn't loosen it up? Try this: When you are done using the glue squeeze a small amount of glue out of tube then cap tightly. Then roll tube up from the bottom. This will remove all the air from inside the tube and the tip, which is what causes the glue to harden. The next time you go to use it, it will be like a new tube!

Does your Thin-Set dry quickly, get grainy and unusable? Try this: Mix a small amount of thinset as you normally would, then scoop it into a small Ziploc baggie and seal it (squeeze the excess air out of the bag first). Cut a small corner off the baggie (one of the corners without the zipper on it) and squeeze out your thinset! When not in use, place the baggie on its side in a shallow saucer with a few drops of water in it. This will keep the exposed thinset slightly damp. Squeeze the baggie to give your thinset a "stir".

(Info from Wits End Mosaics)

Other options -
For Glass on Glass mosaics, you can use Weldbond or silicone.
Weldbond will take some time to 'cure' and clear.
Clear silicone stays clear.
I have used both.
From KimmyStar

From MrShorty:
I use"E-6000" for inside use, and "UV-6000" for outside use. Both dry clear, and don't get hard. They dry to a rubbery consistency. They work on everything I've tried them on so far, except Styrofoam. It melt Styrofoam.

From Yvonne
Have you used clear Tub &Tile adhesive caulk? I have a clay-pot saucer birdbath stained glass and glass tile out in the yard. [Coming up on 3 yrs]
Used T&T, regular grout and tile sealant its wearing well, I did wax it last Spring but will use a waterproof sealant next time. [because I have it in the shed]